In a hologram recording and reproduction method, particularly in a hologram recording and reproduction method in the field of optical storage systems, an SLM (Spatial Light Modulator) such as, for example, a transmission type liquid crystal panel or a DMD (Digital Micro mirror Device) is used for light intensity modulation, and such intensity modulation that a pattern array of bit 1 (for example, the light intensity=high) and bit 0 (for example, the light intensity=low) is obtained is applied to signal light.
At this time, in the SLM, light intensity modulation is applied at a central portion of the SLM in response to recording data to produce signal light while light is transmitted in the form of a ring around the signal light to produce reference light, for example, in such a manner as illustrated in FIG. 2. Then, the signal light modulated in response to the recording data is irradiated upon a hologram recording medium together with the reference light, whereupon interference fringes of the signal light and the reference light are recorded as data on the hologram recording medium.
On the other hand, upon reproduction of data, only the reference light described above is produced by the SLM and is irradiated upon the hologram recording medium to obtain diffraction light corresponding to the interference fringes. An image according to the diffraction light is formed on an image sensor such as, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Oxide Semiconductor) sensor to obtain values of recording bits to carry out data reproduction.
A hologram recording and reproduction method wherein signal light and reference light are irradiated on the same optical axis in this manner is known as a coaxial method.
It is to be noted that, as a related prior art, Nikkei Electronics, Jan. 17, 2005 pp. 106-114 can be listed up.
Here, such a technique of hologram recording and reproduction as described above is expected as a large capacity data storage technique of the next generation which is to replace various optical disk media, an HDD (Hard Disc Drive) and so forth which are placed in practical use in the present situation. From this point, it is desired to further increase the data recording capacity as a technique for hologram recording and reproduction.